The present invention generally pertains to drilling and mining processes and, more particularly, but not by way of limitation, to a mining system particularly adapted for the recovery of coal from relatively thin, generally horizontal mineral seams. The present invention further pertains to cutting heads for such a mining system.
The recovery of coal from coal seams has been the subject of technical development for centuries. Among the more conventional mining techniques, hydraulic mining systems have found certain industry acceptance. Hydraulic mining typically utilizes high pressure water jets to disintegrate material existing in strata or seams generally disposed overhead of the water jets. The dislodged material is permitted to fall to the floor of the mining area and is transported to the mining surface via gravity and/or water in a flume or slurry pipeline. Along these lines, certain developments in Russia included a series of hydro-monitors capable of extracting a strip of coal 3 feet wide and 30 to 40 feet in depth within a matter of minutes. The units were designed to be conveyed on a track to the advancing coal face for extracting the coal. The coal would flow downwardly and be transported to the surface via a flume. Similar techniques to this have found commercial acceptance in China, Canada, and Poland, but only limited attempts have been made to use these techniques in the United States.
Although not as widely accepted in the United States, hydraulic mining methods have been the subject of numerous U.S. patents. U.S. Pat. No. 3,203,736 to Anderson describes a hydraulic method of mining coal employing hydraulic jets of water of unusually small diameter to cut the coal. Such techniques would be particularly applicable to steeply dipping coal seams. Likewise, U.S. Pat. No. 4,536,052 to Huffman describes a hydraulic mining method permitting coal removal from a steeply dipping coal seam by utilizing a vertical well drilled at the lowest point of the proposed excavation. Another slant borehole is drilled at the bottom of the coal seam to intersect with the vertical well. High pressure water jets are then used to disintegrate the coal in a methodical fashion with the resulting slurry flowing along the slant borehole into the vertical well. Once in the well, this coal slurry could be pumped to the surface of the mine. While effective in steeply dipping coal seams where gravity would allow the slurry to flow to the vertical well, other techniques would be necessary for more horizontally oriented mining systems. Additionally, U.S. Pat. No. 4,878,722 to Wang teaches the use of water jets to remove horizontal slices of coal within a seam. Through the sequential mining of layers in this manner from top to bottom, the entire seam of coal can be extracted and the mine roof subsides onto the floor without need for artificial roof support.
Another technique for extracting minerals from subterranean deposits is the above referenced borehole mining. Such techniques create minimal disturbance at the mining surface while water jets are used to cut or erode the pay zone and create a slurry down hole. A sump is created below the pay zone to collect the produced cuttings and slurry, which is transported to the surface via a jet or slurry pump. A wide variety of minerals, primarily soft rock formations, may also be mined utilizing this technique. A more recent borehole mining technique is described in U.S. Pat. No. 3,155,177 to Fly wherein a process for under reaming a vertical well and a hydrocarbon reservoir is shown. The technique illustrated therein utilizes electric motors to convert the apparatus from drilling to under reaming.
More conventional techniques are seen in U.S. Pat. Nos. 4,077,671 and 4,077,481 to Bunnelle which describe methods of and apparatus for drilling and slurry mining with the same tool. A related borehole mining technique is shown in U.S. Pat. No. 3,797,590 to Archibald which teaches the concept of completely drilling the vertical well through the portion of the strata to be mined. Separate lines are used for water jet cutting and slurry removal. A progressive cavity pump is used to tort slurry to the surface. In the later improvement (U.S. Pat. No. 4,401,345) the cutting tool is moved independently from the pumping unit. Later developments shown in U.S. Pat. No. 4,296,970 describe the use of various types of rock crushers at the inlet of the jet pump. A feed screw on the bottom of the drill string is used to meter the flow of slurry into the orifice of a venturi in association with the rock crusher. In a subsequent development (U.S. Pat. No. 4,718,728), it is suggested to use a tri-cone bit assembly on the end of the tool to reduce the particle size to allow slurry transport. In U.S. Pat. No. 5,197,783 an extensible arm assembly is incorporated to allow the water jet cutting mechanism to extend outwardly from the borehole mining tool to provide more effective cutting in the water filled cavity.
The above described mining techniques present methods of and apparatus for mineral excavation for sites with specific geological characteristics. In the main such characteristics include steeply dipping coal seams and/or gravity to facilitate transport of the coal to the surface. Transport of the coal, however, is not the only design problem. The distance between the cutting face and the water jet unit increases as material is eroded away. Cutting effectiveness therefore decreases until the unit is moved. These specific design points have been referred to above and are areas of continued technical development. This is particularly true due to the fact that in borehole mining, cutting effectiveness of the water jets also decreases as the cavity becomes larger in size. When the cavity reaches a point that cutting effectiveness diminishes, either another vertical well must be installed to initiate another cavity or the cutting unit needs to be moved closer to the coal face. Also, when a cavity is creed in unconsolidated material, subsidence may be created and the cavity may collapse. Borehole mining is, therefore, referred to as a selective mining technique and may not always be suitable for low cost extraction on a large scale basis.
In addition, although hydraulic mining techniques have proven effective in the cutting of certain seams of coal, water jets or other hydraulic cutting systems may not cut effectively when rock strata are present within the coal seam. The presence of rock strata often requires that a prohibitively high water pressure be supplied to the water jets to cut the rock bands, requiring too much horsepower for economic coal extraction of the system.
Another conventional technique for extracting minerals from subterranean deposits is a scroll auger. Scroll augers have been used to mine relatively thin, generally horizontal seams of coal. Scroll augers typically include a cylindrical auger used to transport cut coal away from a cutting head located on the front of the auger. The cutting head typically cores and breaks coal by using mechanical bits on the circumference and center of a hollow cylinder located on the front of the auger. The auger and cutting head are rotated, and advanced into a coal seam, using a conventional auger drill unit that is coupled to the rear of the auger. The scroll auger and auger drill unit are positioned on a high wall bench on the surface or in some cases underground within a subterranean access tunnel adjacent a coal seam. Using such a system, adjacent boreholes may be drilled from the high wall bench or access tunnel into the coal seam.
However, scroll augers cannot be efficiently steered, and therefore such scroll augers tend to migrate into adjacent boreholes or out of the coal seam altogether. In addition, as the cutting head advances away from the drilling unit, more and more power is required to thrust by putting weight on the cutting head and for torque to turn the auger. For both of these reasons, the length of the borehole, and thus the length of a particular section of the coal seam actually mined, are typically limited to distances of less than three hundred feet. Therefore, numerous, expensive high wall benches or access tunnels may be required to mine a given seam of coal.
Cutting heads having both water jets and mechanical-type bits have also been utilized for a certain applications. Some of these cutting heads are typically used for the drilling of oil and gas wells. For example, U.S. Pat. No. 4,723,612 discloses a rotating diamond bit that has a cutting face including a plurality of cutters and nozzles. The nozzles direct water in a fan-like pattern that impinges directly onto the cutters, preventing the overheating or clogging of the cutters. U.S. Pat. No. 4,494,618 provides another example of a drill bit having diamond cutting elements and nozzles that are removable, replaceable, and self cleaning. As a further example, U.S. Pat. No. 3,645,346 discloses an erosion drilling system having at least two sets of high pressure water jet nozzles for primary cutting and to counteract nozzle erosion, and auxiliary cutting devices such as cone cutters, drag bit blades, or diamond head cutters.
Other ones of these cutting heads have been used for mining applications. For example, U.S. Pat. No. 4,733,914 discloses a rotating drum type cutting head having both cutter picks and nozzles for delivery of high pressure water to the cutter picks. U.S. Pat. No. 4,765,686 discloses a rotable cutting bit for a mining machine having a hard insert and nozzles for ejecting water from the bit.
U.S. Pat. No. 2,218,130 provides an example of a cutting head having both water jets and cutter blades used for the removal of solids, such as coke, from a vessel or oven. The water jets and cutter blades are used to drill successively larger diameters holes so as to xe2x80x9cream outxe2x80x9d the solids from the vessel.
Despite the above-described conventional mining systems and cutting heads, a need still exists in the mining industry for a reliable cutting head that is capable of economically mining relatively thin, generally horizontal coal (or other mineral) seams. The introduction of high pressure fluid to complement and cut independently with the mechanical cutting bits allows a reduction of the size of the downhole electric motor and required mechanical horsepower. This is critical in thin seams to allow adequate clearance. Furthermore, introduction of high pressure fluid can allow delivery of sufficient horsepower for maximum penetration. In addition, a need also exists for a cutting head that provides improved cutting rates and navigation within relatively thin, generally horizontal coal seams. Furthermore, a need exists for a cutting head for a mining system that addresses the limitations of the above-described conventional cutting heads.
One aspect of the present invention comprises a cutting head for creating an excavation in a mineral seam. The cutting head includes a first body having a manifold for containing high pressure fluid and an axis of rotation generally parallel to the borehole, a first plurality of mechanical bits disposed on the first body, a first plurality of nozzles disposed around the axis of rotation for spraying the high pressure fluid, and a plurality of tubes fluidly coupling the manifold and the first plurality of nozzles. On supplying high pressure fluid to the manifold and rotating the cutting head about the axis of rotation, the nozzles create a generally circular, independent and, as appropriate, overlapping patterns of high pressure fluid jet arcs that cut in front of the cutting head. The pattern of high pressure fluid is directed to cut the borehole independently of the mechanical bits.
In another aspect, he present invention comprises a cutting head for creating an excavation in a mineral seam. The cutting head includes a first body having a manifold for containing high pressure fluid and an axis of rotation generally parallel to the borehole, a plurality of nozzles disposed around the axis of rotation for spraying the high pressure fluid, and a plurality of tubes fluidly coupling the manifold and the first plurality of nozzles. On supplying high pressure fluid to the manifold and rotating the cutting head about the axis of rotation, the nozzles create a generally circular, overlapping pattern of high pressure fluid in front of the cutting head. The pattern of high pressure fluid is directed to cut across substantially an entire face of the cutting head.
In a further aspect, the present invention comprises a method of creating an excavation in a mineral seam. A cutting head is provided. The cutting head has a manifold for containing high pressure fluid, an axis of rotation generally parallel to the borehole, a plurality of mechanical bits disposed at various radii around the axis of rotation, and a plurality of nozzles disposed at various radii around the axis of rotation for spraying the high pressure fluid. The cutting head is positioned proximate a mineral seam, and high pressure fluid is supplied to the manifold. The cutting head is then rotated about the axis of rotation to create a generally circular, overlapping pattern of high pressure fluid in front of the cutting head. The borehole is cut with the rotating pattern of high pressure fluid and the mechanical bits. The high pressure fluid cuts the borehole independently of the mechanical bits.
In a further aspect, the present invention comprises a method of creating an excavation in a mineral seam. A cutting head is provided. The cutting bead has a manifold for containing high pressure fluid, an axis of rotation generally parallel to the borehole, and a plurality of nozzles disposed at various radii around the axis of rotation for spraying the high pressure fluid. The cutting head is positioned proximate a mineral seam, and high pressure fluid is supplied to the manifold. The cutting head is rotated about the axis of rotation to create a generally circular, overlapping pattern of high pressure fluid in front of the cutting head and across substantially an entire face of the cutting head. The borehole is cut with the rotating pattern of high pressure fluid.
In a further aspect, the present invention comprises a cutting head system for creating an excavation in a mineral seam. The cutting head system includes a first cutting head having a manifold for containing high pressure fluid, an axis of rotation generally parallel to the borehole, a plurality of nozzles disposed at various radii around the axis of rotation for spraying the high pressure fluid, and a plurality of hollow tubes fluidly coupling the manifold and the first plurality of nozzles. The cutting head system further includes a second cutting head substantially identical to the first cutting head having a second axis of rotation generally parallel to the excavation, where the second cutting head is arranged in a generally linear fashion with the first cutting head. On supplying high pressure fluid to the manifolds, rotating the first cutting head about the axis of rotation, and rotating the second cutting head about the second axis of rotation, the nozzles on the first and second cutting heads create two adjacent, generally circular, overlapping patterns of high pressure fluid in front of the cutting heads for cutting the excavation with a generally oval-shape cross-section.
In a further aspect, the present invention comprises a cutting head system for creating an excavation in a mineral seam. The cutting head system includes a first cutting head having a manifold for containing high pressure fluid, an axis of rotation generally parallel to the excavation, a plurality of nozzles disposed at various radii around the axis of rotation for spraying the high pressure fluid, and a plurality of hollow tubes fluidly coupling the manifold and the first plurality of nozzles. The cutting head system further includes a second cutting head substantially identical to the first cutting head having a second axis of rotation generally parallel to the excavation, and a third cutting head substantially identical to the first cutting head having a third axis of rotation generally parallel to the excavation. The first, second, and third cutting heads are arranged in a generally triangular arrangement. On supplying high pressure fluid to the manifolds, rotating the first cutting head about the axis of rotation, rotating the second cutting; head about the second axis of rotation, and rotating the third cutting head about the third axis of rotation, the nozzles on the first, second, and third cutting heads create three generally circular, overlapping patterns of high pressure fluid in front of the cutting heads and for cutting the excavation with a generally pie-shaped cross-section.